1. The Field of the Invention
The present invention relates to apparatus, systems, and methods for forming dental appliances. More specifically, the present invention is directed to an apparatus, system, and method for readapting a dental appliance to closely conform the shape of the dental tray to the teeth of a patient with the use of a vacuum forming device.
2. The Relevant Technology
Dental appliances are frequently used in dentistry for such applications as bleaching, fluoridizing, treatments of caries diseases, mouth guards, night guards, bite adjustor trays, and registration bases. It is necessary that dental appliances be well fitted to closely conform to the teeth of the patients on which they are to be worn. Improperly fitting dental appliances tend to irritate the gums, are difficult to retain on the teeth and gums, and may allow treatment substances contained within them to leak out into the mouth of the wearer.
The dental field currently uses a procedure of forming dental appliances and of adapting them to fit the teeth on which they are to be worn that involves the use of a vacuum forming device. Under this procedure, the dental appliances are formed from a sheet of thermoplastic material by creating a model of the teeth, heating the thermoplastic sheet, and vacuum forming the thermoplastic sheet to the model. Once formed, the dental appliance is removed from the model and the excess plastic is trimmed away. The initial removal from the model and subsequent trimming cause distortion of the dental appliance. In order to remedy the distortion, a second procedure, known as readaptation, is commonly performed. As will be seen, certain inherent difficulties make current readaptation procedures unsatisfactory.
In order to better understand the present invention, the presently known manner of forming a dental appliance to fit a person's teeth with the use of a vacuum forming device will now be described. A representative vacuum forming device is shown in FIGS. 1 and 2, and is available from Ultradent Products, Inc., South Jordan, Utah. The depicted vacuum forming device 10 comprises a body section 12 having located therein a vacuum pump 14 for providing a negative pressure. A vacuum forming table 26 is formed on the body section 12 over the vacuum pump 14. The vacuum forming table 26 is provided with holes 44 leading to the vacuum pump 14 and linked in negative pressure communication therewith. A glide rail 18 extends upward from the body section 12, and a hood 20 containing a heating element 22 is located at the top of the glide rail 18. A two-piece clamping frame 24 is slidably attached to the glide rail 18, such that objects held in the clamping frame 24 may be moved into proximity with the heating element 22, and thereafter quickly relocated to the vacuum forming table 26. The clamping frame 24 is attached to one end of a guide rod 28, and the other end of the guide rod 28 is inserted into a sleeve 30 formed in the body section 12. Adjacent to the sleeve 30 is a perpendicular recess 32 containing a spring-loaded ball mechanism 34. The spring-loaded ball 34 presses against the guide rod 28, and when the clamping frame is raised to a given position close to the heating element, inserts itself into an indentation 36 on the surface of the guide rod 28. Once inserted into the indentation 36, the spring-loaded ball mechanism temporarily maintains the guide rod 28 and the clamping frame 24 in the given position. The application of a sufficient downward force on the clamping frame 24 by the operator overcomes the engagement of the spring-loaded ball with the indentation 36, releasing the clamping frame 24 to move freely.
The clamping frame 24 comprises an upper frame 38 and a lower frame 40 connected with hinges 54. A pair of clamps 52 located at either side of the clamping frame 24 are for clamping the upper frame 38 and the lower frame 40 together, such that a square thermoplastic sheet 42 can be retained within the clamping frame 24. The thermoplastic sheet 42 is typically about four inches in dimension on each side, and is made of material such as polypropylene. The clamps 52 of the depicted device comprise S-clamps, and are capable of generating a constant clamping pressure for sheets of varying thicknesses. An indicator light 46 indicates when the heating element 22 is activated, and an on/off switch 48 activates the heating element 22 and the vacuum pump 14. When the on/off switch 48 is activated, sensors on the device detect the position of the clamping frame. The heating element 22 is enabled when the clamping frame 24 is moved to the given position close to the heating element, and the vacuum pump 14 is enabled when the clamping frame 24 is relocated to rest on the vacuum forming table 26.
The method known in the art of vacuum forming a dental appliance using the described vacuum forming device 10 comprises creating a model 50 in the shape of a set of teeth or gums on which the appliance is to be worn, and then placing the model 50 on the vacuum forming table 26. The thermoplastic sheet 42 is then retained within the clamping frame 24, and the S-shaped clamps 52 of the clamping frame 24 are engaged to clamp the thermoplastic sheet 42 in place. The clamping frame 24 is then positioned close to the heating element 22, as shown in FIG. 1. The spring-loaded ball 34 inserts itself into the indentation 36 in the guide rod 28, with a force sufficient to temporarily maintain the clamping frame 24 in the proper vertical position.
The heating element 22 is then activated by pressing on/off switch 48. Once the thermoplastic sheet 42 is sufficiently heated, it will sag below the clamping frame 24 as shown. When the thermoplastic sheet 42 sags to a proper level, typically where the center of the thermoplastic sheet 42 is about two inches below the level of the frame, the thermoplastic sheet 42 is sufficiently thin and pliable to be formed to the model 50. The clamping frame 24 is then pulled down to rest on top of the vacuum forming table 26, as shown in FIG. 2, and the vacuum pump 24 is automatically activated. Negative pressure from the vacuum pump 14 draws the thermoplastic sheet 42 tightly over the model 50, causing the thermoplastic sheet 42 to closely conform to the model 50 as it cools.
After a sufficient amount of time has passed for the thermoplastic sheet 42 to form to the model 50 and cool sufficiently to retain its shape, the vacuum pump 14 is switched off, and the model 50 and the newly formed dental appliance 54 are removed. The outer portion of the excess plastic around the dental appliance 54 is then trimmed from the dental appliance with a set of utility vinyl cutters 56, as shown in FIG. 3. The dental appliance is then separated from the model 50, and the remaining excess plastic is trimmed away with scalloping scissors 57, as shown in FIG. 4. When finished, the dental appliance 54 properly covers only the teeth, with the portions extending above or below the teeth having been removed. As a final step, a flame torch 58 is used to polish and smooth the edges of the dental appliance 54, as shown in FIG. 5.
As mentioned, the initial removal of the dental appliance from the model causes distortion of the dental appliance. Trimming the dental appliance to fit the teeth also causes distortion. A distorted appliance 54 is shown in FIG. 5. Distorted dental appliances tend to fit less tightly around the base of the teeth. Edges protrude and irritate the gums, and the dental appliance loosens at the base of the teeth. Consequently, any treatment materials carried within the dental appliance, such as bleaches or fluorides will tend to leak from the dental appliance into the mouth of the wearer. The resulting disadvantages can be readily appreciated. For instance, the treatment materials are often foul tasting, may irritate the gums of the wearer, or may cause other undesired effects. Furthermore, such leakage is inefficient and wasteful, driving up the cost of dental procedures. To remedy this problem, readaptation methods are commonly used in order to provide the dental appliances with a better fit to the mouth of the wearer.
3. Prior State of the Art
In the past, readaptation has been accomplished with the use of a flame torch. The flame torch typically comprises the small, hand-held, gas-powered torch 58 of FIG. 5. Since the thermoplastic materials used in forming dental appliances are too soft for rotary polishing, one function of the flame torch 58 has typically been to polish the dental appliances and smooth its edges, as previously mentioned. Readaptation has also been accomplished with the use of the flame torch 58 using a procedure of heating the dental appliance 54 on the model 50, as shown in FIG. 5, and then manually forming the dental appliance 54 into place as it cools. The forming of the dental appliance into place is typically accomplished by dipping a finger into a reservoir of water and then pressing the finger to the dental appliance 54, holding the dental appliance in place on the model 50 as the model 50 is cooled by the water. This process of heating and pressing on the dental appliance 54 is repeatedly carried out until the dental appliance 54 conforms more closely to the model 50. As is apparent, a major disadvantage to this process is that it is very time consuming. Furthermore, it is difficult, if not impossible, using this process, to cause the dental appliance 54 to conform precisely to the model 50, and thus to the teeth of the wearer. A readapted dental appliance 54 is shown in FIG. 6.
Other dental procedures are known to have used vacuum forming to create and fit related devices. For instance, a procedure was used in the early seventies by students at the Loma Linda Dental College in California to form registration bases for dentures. The procedure comprised the use of a vacuum device fixed to a cabinet. The registration bases were formed on an X-shaped opening located over the vacuum device. A cylinder with a rubber dam tightly fastened to the cylinder was used as a method of conforming the registration bases to casts of the wearer's gums. The registration bases were formed from a resin based material called shellac that achieves plasticity with low amounts of heat. In the procedure, the shellac material was heated with a heat lamp and placed over the cast of the gums, and the rubber dam, tautly stretched on the cylinder, was placed over the shellac material. The rubber dam was drawn by negative pressure down over the registration base, conforming the shellac material to the cast as the registration base cooled.
While this procedure worked sufficiently for the desired purpose, it was never contemplated for the use of forming dental appliances to fit models of teeth. As then known, the tightly stretched rubber dam worked sufficiently on models of gums, but it was used only with highly plastic materials that are very malleable with low amounts of heat, was used only with casts of gums, and would be inadequate for use with the thermoplastic materials used today. Such modem thermoplastics require more heat in specific amounts, and are not as malleable as the Shellac material. Furthermore, models of teeth have deep embrasures between the representations of teeth, and greater contours than models of gums. The tight fitting rubber dam of this method would not be able to conform to those embrasures and contours, especially using modem thermoplastics, and thus could not produce a dental appliance that properly fits a set of teeth. Part of the present invention, as will later be seen, is the discovery that this process could be modified for the readaptation of dental appliances.
From the above discussion, it can be seen that a need exists in the art for a method to accompany current adaptation procedures, whereby a dental appliance can be readapted in a manner that is less time consuming than currently known procedures. Such a method is also needed that will provide the dental appliance that will closely correspond to the teeth, such that the dental appliance will not irritate the gums, will not fall off, and will not leak its contents. It would also be advantageous if such a method could be accomplished by utilizing the same vacuum forming table to effect readaptation as was originally used to form the dental appliance.